The present disclosure relates generally to luminescent solar concentrators, including those having geometric and other improvements that provide increased and/or uniform output. It also relates to methods of manufacturing and utilizing such concentrators.
Luminescent solar concentrators, also known as luminescent solar collectors or LSCs, are beneficial for capturing solar energy (direct and diffuse sunlight) for use. The LSCs collect incident radiation over a large surface area and concentrate the energy to its edges where it is collected by photovoltaic (PV) cells.
An LSC usually comprises a collector, such as a flat sheet generally made from an optically transparent or semi-transparent material such as glass, a polymer, or like materials. Dispersed within the planar sheet is a fluorescent dye. The large face of the flat sheet can be considered the collection area. The dye in the flat sheet absorbs the sunlight and, via radiative and non-radiative transfer, emits light at a different, longer wavelength in all directions. A substantial fraction of this light is trapped in the flat sheet and can be transported, via total internal reflection (TIR), to at least one edge of the flat sheet.
The concentration of light from a large surface area to a smaller surface area (the edge) is also known as the “edge glow” effect. Due to this effect, the amount of light (i.e. energy) available at the edge is related to the collection area of the flat sheet. A light energy convertor, such as a silicon photovoltaic cell (or photocell), can be physically and/or optically attached to the at least one edge to convert the light energy transmitted thereto into electricity. The electricity can then be transported by wires, electrical leads, etc., from the photovoltaic cell to a desired location.
The cost of an LSC can be measured in terms of dollars per watt peak ($/Wp). One of the most expensive components of the LSC is the photovoltaic cell (PV cell). Hence, the cost of an LSC can be minimized by reducing the amount of silicon per watt of electric power output. Alternatively, the electric power output can also be increased. The electric power output is a function of the optical efficiency and concentration ratio of the collector. Optical efficiency is the percentage of the optical output available to illuminate the photovoltaic cell for any given amount of solar input. Concentration ratio is the ratio of the surface area of the output (i.e. the edge) to the surface area of the input (i.e. the collection area).
Generally, both high optical efficiency and high concentration ratio are desired. A high concentration ratio suggests a design that has a large collection area. However, a large collection area generally means the photons in the center of the collection area must travel a long distance to the photovoltaic cell. This reduces optical efficiency as those photons travel through the medium of the collector and are either absorbed or reflected away from a path that eventually arrives at the edge. On the other hand, a low concentration ratio requires greater usage of silicon.
Mechanical performance requirements must also be met. For example, for forming the collector, the polymer poly(methyl methacrylate) is good for light transmission (i.e. high optical efficiency), but lacks impact resistance and flame retardance, especially at high temperatures, and is thus difficult to use. Polycarbonate has good mechanical properties for producing the flat sheet, but has a lower optical efficiency, limiting its useful size and thus the concentration ratio.
In addition, the photovoltaic cell must be optically coupled to the collector. The photovoltaic cell, which is generally mostly silicon, is usually much more fragile than the collector, which is mostly polymeric. In particular, the materials have very different coefficients of thermal expansion (CTE). In other words, when exposed to heat, they expand at different rates. This mismatch must be accounted for to ensure that the photovoltaic cell does not break as the two components change dimensions. Other failure means, such as corrosion and delamination, also potentially exist.
There is a need for durable luminescent solar concentrators having geometric and other improvements that provide for increased performance.